Methane is by far the least reactive and the most abundant member of the hydrocarbon family with known reserves similar to that of petroleum. Thus, the selective oxidative functionalization of methane to useful chemical products in high conversion and selectivity is of considerable practical importance. Most of the work in this area has involved homogeneous and heterogeneous catalysis by metal species. While there have been some notable successes, none of the systems have demonstrated the optimal combination of selectivity and yield that allows commercialization. Using potassium persulfate as an initiator, the present inventors demonstrate the sulfonation of methane in fuming sulfuric acid.